In recent years, various techniques for increasing the speed of wireless access have been proposed and standardized, with the intention of realizing faster wireless packet communications. It has been said that, in a “Beyond 3G/4G” cellular system, it is possible to achieve a wireless transmission speed of hundreds of megabits per second (Mbps) to 1 gigabits per second (Gbps). When wireless transmission is realized at such a high speed, the transmission power becomes an issue. Thus, it is predicted that an area covered by each cell will become smaller than an area covered by each conventional cell. Also, because each cell will become smaller, it is predicted that the number of base stations that perform wireless communications with terminals will further increase in the future.
The number of base stations and the number of cells that a base station control device is able to accommodate are limited due to constraints related to control specifications and the capacity of the device. As a result, there is a situation in which, even if a base station control device is supposed to be able to accommodate base stations according to the processing capacity thereof, the base station control device is not able to accommodate some of the base stations due to the limitations regarding the number of accommodated base stations and the number of accommodated cells mentioned above. In such a situation, there is a problem in that base station accommodating efficiency of the base station control device is low.
A technique disclosed in Patent Document 1 listed below solves the problem discussed above. In specifically, according to the disclosed technique, a base station line concentrator is provided between a plurality of base stations and a base station control device that controls the base stations. The base station line concentrator converts and transmits control data and user data between the base station control device and the base stations. According to this technique, the base station control device is able to operate while regarding the plurality of base stations as one virtual base station. Consequently, by connecting a plurality of base station line concentrators to a base station control device, it becomes possible to accommodate a larger number of base stations without introducing a new base station control device that is expensive.
The Third Generation Partnership Project (3GPP) has been researching a next-generation wireless access method called Evolved Universal Terrestrial Radio Access (E-UTRA) and a wireless access network called Evolved Universal Terrestrial Radio Access Network (E-UTRAN) that are obtained by optimizing a third-generation wireless access method and a wireless access network called Universal Terrestrial Radio Access Network (UTRAN) for wireless packet communications so as to achieve a lower delay and a higher data rate (see Non-patent Document 1 listed below). In an architecture adopted by E-UTRAN, a wireless network control device called a “Radio Network Controller (RNC)” that controls base stations called “Node B's” is eliminated and base stations called “Evolved Node B's (eNodeB's)” each having the functions of the RNC are directly accommodated while being subordinate to a gateway device called a “System Architecture Evolution Gateway (SAE-GW)” that is provided between a core network and a wireless access network. In this arrangement, because the architecture in which hierarchical structures have been eliminated is adopted into the wireless access network, E-UTRAN is able to achieve advantageous effects where end-to-end delays are reduced and where the network configuration is simplified.    Patent Document 1: Japanese Patent Application Laid-open No. 2006-279261    Non-patent Document 1: 3GPP Technical Specification (TS) 36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2,” Version 8.0.0 (2007-03)